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Shutting Down One Engine After Landing

Q: I’ve noticed a quirk in Continental’s taxiing procedure: it seems that immediately after landing they shut down one of the plane’s engines. Is this my imagination, or is it another cost-cutting strategy? Is that much fuel really burned while taxiing?

Airlines have been doing this for decades, though nowadays they’re quicker than ever with the cut-off levers. With oil prices hanging near $50 a barrel — the cost of jet fuel rose 56 percent between 2003 and 2004, peaking at almost $1.60 a gallon last October — airlines have become hard-edged conservationists of sorts. Planes will routinely taxi in, and out, with a powerplant shut down, the remaining engine(s) and auxiliary power unit (APU) supplying air conditioning, hydraulics and electrics. On a two-engine aircraft, the lowest power setting, a.k.a. “idle thrust,” from one motor is usually enough, or almost enough, to keep it taxiing. Idle thrust from both engines often wastes energy by requiring crews to ride the brakes.

To pick one, the MD-80, a twin-engine narrowbody with seating for about 140, will save 2.4 gallons per minute on a single-engine taxi. If a trip to or from the runway takes seven minutes (hopeful in many cases), that’s close to 34 gallons per flight (17 per taxi in/taxi out). Using the January 2005 average price per gallon of $1.30 presents a savings of about 44 dollars. Assuming an MD-80 flies three legs in a day, that’s $132 per day, per aircraft. For a carrier like American Airlines, with more than 350 MD-80s in its fleet, the saving would be at least $46,000 per day, and more than $16 million a year, on that model alone.

Theoretically anyway. American claims it saved $2 million last year through increased use of single-engine taxiing. As you might expect, such procedures aren’t always practical or possible. The rules vary markedly between airline and aircraft type, and are subject to a slew of fine print — weather conditions, mandatory cool-down or spool-up times, etc.

The price of jet fuel, much like that of automobile gasoline, varies from region to region, airport to airport. A gallon in Houston might run five cents less than New York; a gallon in Singapore a nickel cheaper still; subject to any number of local taxes, fees, and add-ons. This is one of the reasons planes sometimes “tanker” extra fuel between cities.

After considering ETOPS and single-engine taxi, undoubtedly a number of people will be wondering about something, so allow me to make the following declaration: Under no circumstances whatsoever do crews shut down engines during flight to save money.

This Q&A is part of a collection that originally appeared on Patrick Smith, 38, is an erstwhile airline pilot, retired punk rocker and air travel columnist. His book, Ask the Pilot (Riverhead) was voted “Best Travel Book of 2004” by Patrick has traveled to more than 55 countries and always asks for a window seat. He lives near Boston.